The present invention relates to an apparatus and method which convert the acoustic-signal reproducing speed by processing a small amount of data.
Various techniques of converting the speed of reproducing digital PCM acoustic signals from a given recording medium are known. Of these techniques, a method such as redundant addition wherein the motion of a pointer is controlled, PICOLA (Pointer Interval Controlled Over Lap and Add) is generally utilized.
A reproducing-speed converting apparatus will be described, which generates R-fold acoustic signals from source acoustic signals by means of redundant addition achieved by controlling the motion of a pointer (PICOLA system). R is a constant that represents the rate of converting the reproducing speed. R is greater than one (R greater than 1) in the case of high-speed reproduction of acoustic signals. R is equal to or less than one in the case of low-speed reproduction of acoustic signals. FIG. 1 is a block diagram showing the reproducing-speed converting apparatus.
The reproducing-speed converting apparatus comprises a data-recording section 1, an input buffer section 2, a pitch-calculating section 3, a process control section 4, a data-operating section 5, and a data-accumulating section 6. The data-recording section 1 records acoustic signals and holds the same. The input buffer section 2 receives an input acoustic signal s1 from the data-recording section 1. The signal s1 (sampled for max. pitch cyclexc3x972) has been generated from a process-start position P. The input buffer section 2 transfers an acoustic signal s2 for finding a pitch, to the pitch-calculating section 3. The pitch-calculating section 3 calculates a pitch cycle s3, which is supplied to the process control 4. Under the control of the process control section 4, the input buffer section 2 transfers a signal s4, to the data-operating section 5. The data-operating section 5 performs a prescribed process on the signal s4 to achieve high-speed reproduction or low-speed reproduction, thereby generating an operation process signal s5. The signal s5 is supplied via the input buffer section 2 to the data-accumulating section 6. In the meantime, the process control section 4 supplies a process control signal s6 to the input buffer section 2. Further, the process control section 4 supplies a data-read control signal s7 to the data-recording section 1.
How the conventional reproducing-speed converting apparatus, which is a PICOLA system, accomplishes high-speed reproduction and how-speed reproduction will be described below.
The high-speed reproduction will be first explained, with reference to FIGS. 2 to 4. First, of the acoustic signals held in the data-recording section 1, an input acoustic signal s1 (sampled for max. pitch cyclexc3x972) is read from the process-start position P shown in FIG. 2, into the input buffer section 2. The signal s1 is transferred from the section 2 to the pitch-calculating section 3.
The pitch-calculating section 3 calculates a pitch cycle s3. More specifically, the section 3 generates a pitch cycle s3 (T0) that mininimizes the mean distortion d (T) defined by the following equation (1):
(Equation 1)                                           d            ⁡                          (              T              )                                =                                    1              T                        ⁢                                          ∑                                  i                  =                  0                                                  T                  -                  1                                            ⁢                              xe2x80x83                            ⁢                                                {                                                            x                      ⁡                                              (                        i                        )                                                              -                                          x                      ⁡                                              (                                                  i                          +                          T                                                )                                                                              }                                2                                                    ,                              T            min                    ≤          T          ≤                      T            max                                              (1)            
The input buffer 2 transfers an acoustic signal, or a signal s4, to the data-operating section 5. The signal s4 is based on the pitch cycle s3 (T0) the pitch-calculating section 3 has calculated in accordance with the equation (1). The signal s4 lasts for 2 pitch cycles from the process-start position P.
The acoustic signal s4 lasting for 2 pitch cycles (2xc3x97T0), read into the data-operating section 5, is subjected to weight-adding process that is performed in accordance with the weight-window data shown in FIG. 3. The section 5 generates a weight-added signal, or an operation process signal a5 that lasts for 1 pitch cycle (T0 sample).
Then, the process control section 4 calculates a length L of a reproduced signal (T0 sample), in accordance with the rate R (R greater than 1) of converting the reproducing speed. The length L is defined by the following equation (2):
(Equation 2)                     L        =                              T            0                    xc3x97                      1                          R              -              1                                                          (2)            
The reproduction-signal length L calculated in accordance with the equation (2) may be longer than the pitch cycle T0 (1 less than R less than 2). In this case, the acoustic signal (i.e., operation process signal s5) generated by the data-operating section 5 and lasting for one pitch cycle (i.e., T0 sample) is transferred to the data-accumulating section 6. Moreover, other input acoustic signals are transferred from the input buffer section 2 to the data-accumulating section 6, so that all samples transferred to the data-accumulating section 6 defined the reproduction-signal length L.
The length defined by the input acoustic signals read into the input buffer section 2 may be shorter than the reproduction-signal length L. If so, other acoustic signals are read from the data-recording section 1 into the input buffer section 2 in accordance with a data-read control signal s7 supplied from the process control section 4. These signals, which are required to make the length equal to the reproducing-signal length L, are directly transferred to the data-accumulating section The reproducing-signal length L may be shorter than the pitch cycle T0 (R greater than 2) as is illustrated in FIG. 4. In this case, the acoustic signals, which are L samples included in T0 samples that define one pitch cycle calculated by the data-operating section 5, are transferred to the data-accumulating section 6.
The next process-start position Pxe2x80x2 in the data-recording section 1 is updated in accordance with the following equation (3):
(Equation 3)                               P          xe2x80x2                =                  P          +                                    T              0                        xc3x97                          R                              R                -                1                                                                        (3)            
The low-speed reproduction will be now explained, with reference to FIGS. 5 to 7. First, of the acoustic signals held in the data-recording section 1, an input acoustic signal s1 (sampled for max. pitch cyclexc3x972) is read from the process-start position P shown in FIG. 5, into the input buffer section 2. The signal s1 is transferred from the section 2 to the pitch-calculating section 3. The pitch-calculating section 3 calculates a pitch cycle s3.
The input buffer 2 transfers an acoustic signal, or a signal s4, to the data-operating section 5. The signal s4 is based on the pitch cycle s3 (T0) the pitch-calculating section 3 has calculated. The signal s4 lasts for 2 pitch cycles from the process-start position P.
The acoustic signal s4 lasting for 2 pitch cycles, read into the data-operating section 5, is subjected to weight-adding process that is performed in accordance with the weight-window data shown in FIG. 6. The section 5 generates a weight-added signal, or an operation process signal a5 that lasts for 1 pitch cycle (T0 sample).
Next, the process control section 4 calculates a length L of a reproduced signal [sample], in accordance with the rate R (0 less than R less than 1) of converting the reproducing speed. The length L is defined by the following equation (4):
(Equation 4)                     L        =                              T            0                    xc3x97                      1                          1              -              R                                                          (4)            
The reproduced-signal length L calculated in accordance with the equation (2) may be longer than two pitch cycles (2xc3x97T0) and, hence (0.5 less than R less than 1). If so, the acoustic signal for one pitch cycle (T0 sample) from the first signal held in the input buffer section 2 is transferred to the data-accumulating section 6, along with the acoustic signal (i.e., operation process signal s5) generated by the data-operating section 5 and lasting for one pitch cycle (i.e., T0 sample). Moreover, other input acoustic signals are transferred from the input buffer section 2 to the data-accumulating section 6, so that all samples transferred to the data-accumulating section 6 define the reproduced-signal length L.
The length defined by the input acoustic signals read into the input buffer section 2 may be shorter than the reproduced-signal length L. Then, other acoustic signals are read from the data-recording section 1 into the input buffer section 2 in accordance with a data-read control signal s7 supplied from the process control circuit 4. These signals, which are required to make the length equal to the reproduced-signal length L, are directly transferred to the data-accumulating section 6.
The reproduce-signal length L may be shorter than two pitch cycles (2xc3x97T0) (that is, R greater than 0.5) as shown in FIG. 7. In this case, the acoustic signals, which are L-T0 samples included in T0 samples that define one pitch cycle calculated by the data-operating section 5 and lasts from the first signal held in the input buffer section 2, are transferred to the data-accunulating section 6.
The next process-start position Pxe2x80x2 in the data-recording section 1 is updated in accordance with the following equation (5):
(Equation 5)                               P          xe2x80x2                =                  P          +                                    T              0                        xc3x97                          R                              1                -                R                                                                        (5)            
The greater part of the calculation performed in the conventional PICOLA system described above is the calculation of pitches in the pitch-calculating section 3. A pitch that would minimize the mean distortion defined by the following equation (1) is searched for by means of the pitch-calculating section 3. The number of samples per unit time of the acoustic signals is increased in the higher sampling frequency. Thus, the pitch cycle for searching is increased.
FIG. 8 represents the relation between the sampling frequency and the averaged processing power (i.e., ratio of processing time to the duration of sound reproduced). As seen from FIG. 8, the amount of data that should be processed to calculate pitch cycles in the conventional PICOLA system is about a square of the sampling frequency.
The present invention has been made in view of the foregoing. The object of the invention is to provide an apparatus and method that convert the speed of reproducing acoustic signals sampled at such a high frequency as 48000 Hz or 44100 Hz, with a smaller amount of data processing compared with the conventional apparatus and method.
To attain the object, an apparatus for converting an acoustic-signal reproducing speed, according to the invention, comprises: recording means for recording and holding acoustic signals; decimation means for performing decimation process on the acoustic signals recorded in the recording means; first accumulating means for accumulating acoustic signals down-sampled by the decimation means; pitch-calculating means for calculating a pitch cycle of the signals accumulated in the first accumulating means; second accumulating means for accumulating the acoustic signals recorded in the recording means; operation means for calculating a similar waveform from a waveform of the pitch cycle calculated by the pitch-calculating means; third accumulating means for accumulating data representing the similar waveform calculated by the operation means; and control means for controlling the reading of data into the second accumulating means, the calculation performed in the operation means, and the transfer of data to the third accumulating means.
A method of converting an acoustic-signal reproducing speed, according to the invention, comprises: a decimation step of performing decimation process on acoustic signals recorded in recording means; a first input-output step of inputting and outputting acoustic signals down-sampled in the decimation step, into and from a first accumulating means; a pitch-calculating step of calculating a pitch cycle of the signals accumulated in the first accumulating means; a second input-output step of inputting and outputting the acoustic signals recorded in the recording means, into and from a second accumulating means; an operation step of calculating a similar waveform from a pitch waveform of the pitch cycle calculated in the pitch-calculating step; and a third input-output step of inputting and outputting data representing the similar waveform calculated in the pitch-calculating step, into and from a third accumulating means.
An apparatus for converting an acoustic-signal reproducing speed, according to this invention, comprises: recording means for recording and holding acoustic signals; decimation means for performing decimation process on the acoustic signals recorded in the recording means; first accumulating means for accumulating, in units of frames, acoustic signals down-sampled by the decimation means; pitch-calculating means for calculating a pitch cycle of the signals accumulated in the first accumulating means; second accumulating means for accumulating, in units of frames, the acoustic signals recorded in the recording means; operation means for calculating a similar waveform from a waveform of the pitch cycle calculated by the pitch-calculating means; third accumulating means for accumulating, in units of frames, data representing the similar waveform calculated by the operation means; and data-position designating means for controlling a position in the second accumulating means, to which acoustic signals are read, a position in the second accumulating means, at which the calculation of the pitch is started, a position in the third accumulating means, to which data is transferred, and a position in the third accumulating means, at which data is recorded.
A method of converting an acoustic-signal reproducing speed, according to the invention, comprises: a decimation step of performing decimation process on acoustic signals recorded in recording means; a first input-output step of inputting and outputting, in units of frames, acoustic signals down-sampled in the decimation step, into and from a first accumulating means; a pitch-calculating step of calculating a pitch cycle of the signals accumulated in the first accumulating means; a second input-output step of inputting and outputting, in units of frames, the acoustic signals recorded in the recording means, into and from a second accumulating means; an operation step of calculating a similar waveform from a pitch waveform of the pitch cycle calculated in the pitch-calculating step; and a third input-output step of inputting and outputting, in units of frames, data representing the similar waveform calculated in the pitch-calculating step, into and from a third accumulating means.
With the present invention it is possible to reduce the amount of data that should be processed to convert the speed of reproducing acoustic signals that have been sampled at such a high frequency as 48000 Hz or 44100 Hz.